Pyrotechnical igniters are known in the prior art which comprise a case formed by a lateral wall comprising an inwardly curved zone and at least one weak zone as is disclosed by the document US2009179408.
The weak zone forms a vent hole on the side wall for freeing gases and pyrotechnical material. This weak zone assumes the shape of a local reduction of the thickness of the side wall. The thickness of the remaining material allows the vent hole to open at a pressure lower than the rupture pressure of the side wall when the interior of the case is subjected to a pressure.
The precision of this reduction of thickness is essential for guaranteeing a repeatable and reproducible functioning between the igniters manufactured and therefore the devices in which they are positioned. A defect in the realising of the weak zone can cause a poor opening of the vent hole, which can bring about a deterioration of the case and a malfunctioning of the device in which it is positioned.
In order to guarantee a good realisation of the weak zone it is known to form a plane zone which is formed on the side surface of the igniter prior to the realising of the weak zone and is sufficiently large to receive the weak zone subsequently in the manufacture of the case. The striking on the plane zone allows the tolerances required for the thickness of the material remaining at the bottom of the weak zone to be achieved. Such tolerances cannot be achieved without a striking of the weak zone on a plane zone.
This manner of proceeding brings it about that a step for realising a plane zone is necessary, which requires complementary tools and brings about maintenance costs. Furthermore, the plane zone reduces the useful internal volume of the case. Finally, the realising of the plane zone causes deformations of the outer case surface. These deformations are problematic;                for the subsequent positioning of an external plastic hood which generally serves to electrically insulate the igniter case from the outer environment of the igniter,        during the insertion of a glass crosspiece which closes the igniter,        during the welding of the case on the glass crosspiece, and        when the igniter receives an overmolding, since the tools must then be defined as properly as possible with the igniter.        